I think that was me. Smoke while heating is usually blue/grey and is oil burning out of the smokebox - Accu locos are renowned for throwing excess oil. When running, it is supposed to come out of the stack BUT only during the exhaust 'event'. You can observe these at low speed - there should be 4 distinct puffs as per a real engine.Someone suggested to me to watch for escaping steam. While the loco is pre-heating there is only a little smoke I assume travelling up the stack but when running there is a subsstantial amount out of the stack.
What we found on an 0-6-0 was that steam was coming out when it wasn't supposed to, If you have lots of steam exhausting, it could be 'blowing by' the valves or pistons and being wasted.